This invention relates generally to a method for providing a desired weight imbalance in a bowling ball and apparatus for impelementing the method and more specifically to a method for accurately locating a reference point on an undrilled bowling ball, or locating finger and thumb holes for a bowler's grip or a balance hole on either an undrilled bowling bowl or a previously drilled bowling ball so as to provide a desired bowling ball imbalance or dynamic balance and apparatus for implementing the method.
All bowling balls are manufactured with a weight block or blocks (hereinafter referred to as a block since the number of blocks is immaterial for an understanding of the present invention) cast in the inner core material of the bowling ball. The purpose of the weight block is to counteract the change in the bowling ball's balance or relative imbalance resulting from drilling the bowling ball for finger and thumb grip holes.
Gripping holes for most bowling balls drilled today are over a manufacturer's label. Assuming that a bowling ball is labelled correctly, the bowling ball will have little, if any, side weight or finger weight but will probably have some top weight. This means that the bowling ball would come to rest with the gripping holes on the bottom if the ball were suspended in a medium such as mercury or on an air table and allowed to reach equilibrium. Wobble is a phenomenon that results from a bowling ball not being dynamically balanced (balanced as it rolls). A bowling ball that has zero side weight, zero finger weight, and zero top weight is said to be balanced statically that is, it weights the same in a dodo scale regardless of which way the bowling ball is positioned in the dodo scale. If a bowling ball has something other than zero for any of three weights, then the bowling ball will wobble as it rolls unless the three weights create a controlled imbalance. If a bowling ball has a controlled imbalance then it is said to be balanced dynamically. A bowling ball that is balanced statically will automatically be balanced dynamically but not the converse. The only exception is a dynamically balanced bowling ball with zero weight difference in three directions, top weight, side weight and finger weight. Instead of rolling smoothly, a dynamically unbalanced bowling ball pulsates as it rolls. This characteristic is usually caused by too much top weight. A relatively small weight can make a noticable difference on a relatively heavy ball.
The goal of operators of bowling ball drilling equipment is to drill a thumb and finger grip holes or a balance hole into a bowling ball relative to the location of the weight block within the bowling ball so that the removal of weight by drilling and the excess weight in the weight block will complement each other thus providing a bowling ball with a desired imbalance or dynamic balance. It should be understood that "desired imbalance" could include a statically balanced bowling ball, in which case the imbalance would be zero.
However, since bowler's handspans are different and fingers and thumbs are different sizes for different bowlers, it is extremely unlikely that material removed by drilling will be exactly offset by the extra mass of the weight block when relying on presently used methods, including trial and error, a driller's skill notwithstanding.
Presently, the actual location of a weight block in a bowling ball is never exactly known due to the lack of refinement in methods used by bowling ball manufacturers to mark a bowling ball at the factory. One method used by manufacturers has a laborer float a number of bowling balls in a mercury bath, spin the bowling balls and then return after the balls have supposedly stopped spinning. The laborer then marks the bowling balls with a "Manufacturer's Reference Point" or MRP.
In theory the MRP indicates the location of the weight block relative to an imaginary line from the geometric center of the bowling ball through the center of gravity of the bowling ball and through the bowling ball's outer surface. The MRP is supposed to indicate the location of an intersection of the imaginary line and the bowling ball surface, also called "center-of-palm". The MRP can be off by a considerable amount but the driller will never know before an incorrectly marked "MRP" bowling ball is drilled and perhaps ruined for a bowler.
Even if a bowling ball has a nearly correct MRP, other errors may be introduced by the driller of the bowling ball so as to offset the mass of the weight block. Drilling finger and thumb grip holes in a bowling ball requires the removal of material from the bowling ball. Drilling finger and thumb grip holes in a bowling ball becomes more of an art than a science, particularly if a bowler requests a particular weight imbalance, since the exact location of the weight block with its extra mass can not be exactly offset by known methods, for example, trial and error. Experience has shown that only through the use of unteachable skill and trial and error may a driller become skilled in the preparation of a bowling ball to meet a bowler's particular requirements and even the experienced driller will not be able to consistently meet the bowler's requirements for weight imbalance.
In addition to the above, the American Bowling Congress has established tolerances that pertain to the imbalance of a bowling ball in order to provide guidelines for acceptable imbalances of drilled bowling balls. Any bowling ball used in a competition sanctioned by the American Bowling Congress must conform to these specifications and nearly all bowling competitions are sanctioned by the American Bowling Congress.
The allowed tolerances have such a wide range that a bowling ball that conforms at one end of the range reacts on a bowling lane or alley much differently than a bowling ball that conforms to the other end of the specified range. The present invention enables each bowler to have a bowler requested desired imbalance (or balance) in his or her bowling ball. Alternatively, the present invention also enables a bowler to have optimum imbalance that may be determined by the present invention corresponding to dynamic balance. Dynamic balance may be determined from the location of a ball track on the surface of the bowling ball. Optimum imbalance refers to a bowling ball that is dynamically balanced.
The present method for providing a desired weight imbalance in a bowling ball and apparatus for performing the method solves these and other problems in a manner not disclosed in the known prior art.